Frequency synthesizer circuits are commonly used in electronic devices. Frequency synthesizer integrated circuits (ICs) may be used, for example, to generate clock signals with user-selectable frequencies for computing, bus communications and other electronics applications.
Some frequency synthesizer ICs may provide jitter attenuation using a dual PLL loop structure. For example, some conventional ICs use dual PLL structure including a fractional-N phase locked loop (PLL) that receives a reference clock signal from a crystal oscillator and another PLL control circuit that receives an input clock signal and generates a control signal that controls a feedback divider of the crystal oscillator-based fractional-N PLL, which provides jitter attenuation. Such a device may also provide frequency translation with respect to the input clock signal. An example of such a device is the IDT8T49N222I FemtoClock® NG Frequency Translator/Synthesizer, described in a data sheet entitled “FemtoClock® NG Universal Frequency Translator” (2012).